The present invention relates to a sheet separating mechanism, adapted to be positioned in an imaging device, such as a printer utilizing a so-called electrophotographic system, for separating a recording sheet from a photoconductive member on which a toner image has been formed. More particularly, the present invention relates to a sheet separating mechanism capable of definitely separating the recording sheet from the photoconductive member when a transfer charger for executing a transfer operation onto the recording sheet is retracted from an operating position thereof.
Conventionally, there has been known an imaging device utilizing an electrophotographic system in which a latent image is formed on a photoconductive member, such as a drum having been evenly charged with a predetermined polarity in advance, toner particles are adhered on a surface of the photoconductive member in accordance with the latent image, i.e., a visible toner image corresponding to the latent image is formed on the photoconductive member, and the toner image is transferred and fixed onto a predetermined recording medium such as a continuous-form recording sheet.
As the imaging device, there is an electrophotographic printer for printing information on a folding type continuous sheet with feed holes, which is called a fan-folded sheet similar to that used in a conventional line printer and the like.
The fan-folded sheet is arranged in such a manner that a boundary between two pages thereof is provided with a perforated tear line along which the sheet is to be cut. Thus, the fan-folded sheet is alternately folded along the perforated tear line in the opposite direction and applied to the imaging device in a stacked state.
Incidentally, a printer using the fan-folded sheet as a recording medium must begin a printing operation for each of the pages at a position separated apart from the perforated tear line by a predetermined distance. That is, the printing operation is started at the position separated apart from a leading edge in a direction along which the printing operations are executed. In the above arrangement of the electrophotographic system, each of operation units utilized therein, i.e., a charging unit, an exposure unit, development unit, and transfer unit, are provided around the photoconductive drum, and each of the units are sequentially put into operation as the photoconductive drum is rotated. Thus, a visible image is transferred onto the recording medium, i.e., fan-folded sheet, when the developed portion of the photoconductive drum at which the visible image is formed gets to a transfer position during the rotation of the photoconductive drum. Therefore, a print start point on the fan-folded sheet must be adjusted by relatively moving, i.e., rotating, the photoconductive drum with respect to the fan-folded sheet. In other words, before the printing operation is executed, it is necessary to control a positional relationship between an image forming start point on the photoconductive drum and the fan-folded sheet in such a manner that the position of the photoconductive drum at which exposure is to be started is coincided with the print start point of each of the pages of the fan-folded sheet.
If the fan-folded sheet is kept in contact with the photoconductive drum, i.e., the sheet is kept in a transfer state, a problem arises in that, during the above-described position adjusting operation, the photoconductive material adhered on the photoconductive drum is scratched or worn to shorten the life of the photoconductive drum, while the fan-folded sheet is stained with toner while remaining on the surface of the photoconductive drum. To cope with this problem, there have been prior art systems, for retracting the transfer charger from the operating position thereof at which the transfer charger causes the fan-folded sheet to be contacted with the photoconductive drum, for example, as disclosed in, Japanese Patent Provisional Publication HEI 2-103076. In such conventional charger retracting systems, the transfer charger is arranged to be synchronously retracted from the operating position thereof with cease of a feeding operation of the fan-folded sheet and, further returned to the operating position when the exposure start position reaches a transfer position during the rotation of the photoconductive drum.
Nevertheless, a problem arises in that the fan-folded sheet is not definitely separated from the photoconductive drum even if the transfer charger is retracted from the operating position after completion of the printing operation. In other words, since the fan-folded sheet is arranged to be separated from the photoconductive drum only by its own weight, it is often kept in contact with the photoconductive drum even if the transfer charger is retracted. As a result, the fan-folded sheet is stained by the toner when a printing operation is resumed. This problem is more often caused when the folding direction of the perforated tear line on the fan-folded sheet is directed toward the photoconductive drum side. In a low-humidity condition, for example, in winter, the fan-folded sheet and the photoconductive drum are apt to be contacted with each other by so-called electrostatic force therebetween, and the above-described problem is more often caused.